Tried it on another character and the first kill always gives you "Shan'ze Ritual Stone" and some lesser / elder charms, after that, you can keep farming for hours and nothing but lesser charms, I'm trying it right know on a 3rd character
ps : first time killing rare elite on the isle with those characters.
Another question : only the warlock can see / drop / loot the tome or you can farm it on any class ?